Effectiveness of Trichoderma strains isolated from the rhizosphere of citrus tree to control Alternaria alternata, Colletotrichum gloeosporioides and Penicillium digitatum A21 resistant to pyrimethanil in post-harvest oranges (Citrus sinensis L. (Osbeck)).

AIMS: Penicillium digitatum, Alternaria alternata and Colletotrichum gloeosporioides are pathogens responsible for large decays and production losses of citrus. They are commonly controlled by fungicides, whose excessive applications have led to the emergence of resistant P. digitatum strains. Alternative approaches are imperative for sustainable and environmental harmless citrus production, being biological control a promising strategy. The objective was to evaluate the potential of Trichoderma strains native from the rhizosphere of citrus trees to control these pathogens. METHODS AND RESULTS: Seven strains were isolated and identified as Trichoderma harzianum, T. guizhouense, T. atroviride and T. koningiopsis through morphological and molecular analyses. Five of them showed effective antagonist performance in vitro against the pathogens. The strain T. harzianum IC-30 was the best biological control agent in vivo, obtaining a reduction of rot percentage around 80% after 3 weeks of infection of oranges with P. digitatum A21 (resistant to pyrimethanil). This strain also showed the highest chitinase and glucanase activities. CONCLUSIONS: Trichoderma harzianum IC-30 is an optimal antagonist for the control of green mould spreading and other pathogens in post-harvest citrus fruits. SIGNIFICANCE AND IMPACT OF THE STUDY: The strain combined with supplementary practices could lead to sustainable management of citrus fungal diseases, dispensing with synthetic fungicides.

Metagenomics reveals the high polycyclic aromatic hydrocarbon-degradation potential of abundant uncultured bacteria from chronically polluted subantarctic and temperate coastal marine environments.

AIMS: To investigate the potential to degrade polycyclic aromatic hydrocarbons (PAHs) of yet-to-be-cultured bacterial populations from chronically polluted intertidal sediments. METHODS AND RESULTS: A gene variant encoding the alpha subunit of the catalytic component of an aromatic-ring-hydroxylating oxygenase (RHO) was abundant in intertidal sediments from chronically polluted subantarctic and temperate coastal environments, and its abundance increased after PAH amendment. Conversely, this marker gene was not detected in sediments from a nonimpacted site, even after a short-term PAH exposure. A metagenomic fragment carrying this gene variant was identified in a fosmid library of subantarctic sediments. This fragment contained five pairs of alpha and beta subunit genes and a lone alpha subunit gene of oxygenases, classified as belonging to three different RHO functional classes. In silico structural analysis suggested that two of these oxygenases contain large substrate-binding pockets, capable of accepting high molecular weight PAHs. CONCLUSIONS: The identified uncultured micro-organism presents the potential to degrade aromatic hydrocarbons with various chemical structures, and could represent an important member of the PAH-degrading community in these polluted coastal environments. SIGNIFICANCE AND IMPACT OF THE STUDY: This work provides valuable information for the design of environmental molecular diagnostic tools and for the biotechnological application of RHO enzymes.